These studies are aimed at understanding how the human immune system recognizes and destroys foreign cells. Further understanding should lead to new approaches in the therapy of infectious and neoplastic diseases. BIBLIOGRAPHIC REFERENCES: Muchmore, A.V., Koski, I., Dooley, N., and Blaese, R.M.: Artefactual plaque formation in vitro and in vivo due to passive transfer of specific antibody. J. Immunol. 116:1016-1019, 1976. Muchmore, A.V., and Blaese, R.M.: Immunoregulatory properties of fractions from human pregnancy urine: Evidence that human chorionic gonadotropin is not responsible. J. Immunol. 118:881-886, 1977.